Taurine, 2-aminoethanesulfonic acid, is a beta-amino acid highly concentrated in the retina. The loss of a normal level of taurine in the retina leads to visual impediment falling into blindness owing to degeneration of this tissue. the maintenance and control of the taurine concentration in the retina is primarily due to the activity of the taurine transfer in the retinal pigment epithelium, because taurine in the retina is supplied from the choroidal blood circulation through the retinal pigment epithelium. Furthermore, taurine is a neurotransmitter which is released from the retina by light stimulation and taken up promptly by the retina and retinal pigment epithelium. Therefore, the retinal pigment epithelium plays a pivotal role for normal vision via the taurine traffic. This research grant is focused on the mechanisms of taurine transport in the retinal pigment epithelium. Understanding of the regulatory and molecular aspects of taurine transporters in the retinal pigment epithelium of the eye is the main goal which will be achieved in the research project proposed in this grant application. In order to accomplish this goal, five specific aims were assigned to the project as follows: (1) Biochemical characterization of the taurine transporter in the apical membrane of the bovine retinal pigment epithelium, (2) establishment of a procedure for isolation of the basolateral membrane from the bovine retinal pigment epithelium and characterization of taurine transporter in the membrane; (3) characterization of taurine transporter in the cultured human retinal pigment epithelium and elucidation of its biological regulation, (4) reconstitution and purification of the constituent protein of the taurine transporter from the apical membrane of the bovine retinal pigment epithelium, and (5) oocyte expression of the taurine transporter of the human retinal pigment epithelial cells. Accordingly, till the end of the project period, distribution of taurine transporters, characteristics of each transporter available for taurine, and intracellular mechanisms for biological regulation of the taurine transporters will be clarified in the retinal pigment epithelium. Long-term objectives of the project are to comprehend the harmonious regulation of the taurine traffic by the transporters under physiological requirements and their genetic aspects relevant to a clinical condition, retinitis pigmentosa. Achievement of the project will provide understanding of physiological, biological and genetic importance of the taurine transporters for normal vision in the eye.